1. Field of the Invention
The invention is based on a fuel overflow valve for a fuel injection system and on a fuel injection system having a fuel overflow valve.
2. Description of the Prior Art
One such fuel overflow valve and one such fuel injection system are known from German Patent Disclosure DE 100 57 244 1. This fuel overflow valve serves to limit pressure in a low-pressure region of the fuel injection system. The fuel overflow valve has a valve housing, in which a valve member is reciprocatably disposed. By means of the valve member, upon its reciprocating motion, the connection of an inlet from the low-pressure region with an outlet to a relief region is controlled. The valve member is urged by a valve spring in the direction of a closing position in which the connection of the inlet with the outlet is interrupted, and is urged in the opening direction by the pressure prevailing in the inlet. If the pressure in the low-pressure region exceeds the opening pressure determined by the valve spring, the fuel overflow valve opens, and fuel can flow from the inlet out of the low-pressure region via the outlet into a relief region, such as a return to the fuel tank. The fuel injection system has a high-pressure pump, by which fuel is delivered by high pressure to at least one injector at least indirectly, for instance via a reservoir. By means of a feed pump, fuel is delivered to the high-pressure pump. The high-pressure pump has at least one pump piston that is driven in a reciprocating motion by a drive mechanism disposed in a drive region. The low-pressure region of the fuel injection system extends between the feed pump and the high-pressure pump, and in this low-pressure region, a low pressure generated by the feed pump prevails. The low-pressure region communicates with the drive region of the high-pressure pump. Because of the reciprocating motion of the at least one pump piston, the volume of the drive region varies, since in the outlet-oriented stroke of the pump piston, the volume of the drive region is increased, and in the inlet-oriented stroke of the pump piston, the volume of the drive region is decreased. As a result, pressure fluctuations are created in the drive region. Especially in the case of a high-pressure pump with only one pump piston, relatively strong pressure fluctuations are created. As a result, pressure fluctuations are generated in the entire low-pressure region as well, and they can impair the function of the fuel injection system. To compensate for these pressure fluctuations, the valve member of the fuel overflow valve must be capable of executing a long stroke, which accordingly necessitates a long stroke of the valve spring as well. This in turn means that a large amount of space is necessary for the valve spring, and the valve spring is heavily loaded and can therefore break.